1. Field of the Invention
The present invention relates to an inkjet head for ejecting ink onto a recording medium to perform printing.
2. Description of the Related Art
An inkjet head is used in an inkjet printer or the like so that pulse-like pressure is selectively applied to each of pressure chambers supplied with ink from an ink tank to thereby eject ink from a nozzle connected to the selected pressure chamber. An actuator unit which is a laminate of piezoelectric sheets made of piezoelectric ceramics may be used as means for applying pressure to each pressure chamber selectively.
As an example of this type inkjet head, there is known an inkjet head including an actuator unit which has a laminate of continuous planar piezoelectric sheets laid over pressure chambers so that at least one of the piezoelectric sheets is put between a common electrode disposed so as to be common to all the pressure chambers and kept at ground potential and a large number of individual electrodes (i.e. drive electrodes) disposed in positions opposite to the pressure chambers respectively (Please see JP-A-4-341852 (FIG. 1) and U.S. Pat. No. 5,402,159). The portion of the piezoelectric sheet sandwiched between the common electrode and the individual electrodes and polarized in a direction of lamination shrinks and expands in the direction of lamination by a so-called longitudinal piezoelectric effect when an external electric field is applied in a direction of polarization of the piezoelectric sheet in the condition that individual electrodes located on opposite sides of the sandwiched portion are set so as to be different in electric potential from the common electrode. In this case, the portion of the piezoelectric sheet sandwiched between the common electrode and the individual electrodes serves as an active layer capable of being deformed by the piezoelectric effect when an external electric field is applied. As a result, the volume of a corresponding pressure chamber is changed so that ink can be ejected from a nozzle connected to the pressure chamber toward a recording medium.